U.S. patent application number 12/197027 was filed with the patent office on 2010-02-25 for automated method and system for self-calibration of image on media sheets using an auto duplex media path.
This patent application is currently assigned to Xerox Corporation. Invention is credited to John Timothy Howell, Daniel Clark Park.
Application Number | 20100047000 12/197027 |
Document ID | / |
Family ID | 41696532 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100047000 |
Kind Code |
A1 |
Park; Daniel Clark ; et
al. |
February 25, 2010 |
AUTOMATED METHOD AND SYSTEM FOR SELF-CALIBRATION OF IMAGE ON MEDIA
SHEETS USING AN AUTO DUPLEX MEDIA PATH
Abstract
Automated image on media registration and self-calibration using
a built-in printing system duplex media path is enabled. The media
sheet can be registered in a registration system and a calibration
image can be placed on the media sheet after registration of the
media. The media sheet can be inverted in the duplex media path and
re-fed for detection of calibration image placement accuracy on the
media sheet. The registration system can transmit the image
registration placement data to a printer controller. Thereafter,
the printer controller can adjust system settings to compensate for
an image placement registration offset using a calibration
algorithm. The invention enables system adjustments without
requiring manual measurements or media transfer to an independent
scanning device or adding complexity to printing systems.
Inventors: |
Park; Daniel Clark; (West
Linn, OR) ; Howell; John Timothy; (Tigard,
OR) |
Correspondence
Address: |
Xerox Corporation;c/o ORTIZ & LOPEZ, PLLC
P. O. BOX 4484
ALBUQUERQUE
NM
87196-4484
US
|
Assignee: |
Xerox Corporation
|
Family ID: |
41696532 |
Appl. No.: |
12/197027 |
Filed: |
August 22, 2008 |
Current U.S.
Class: |
399/394 |
Current CPC
Class: |
G03G 2215/00067
20130101; G03G 2215/00569 20130101; G03G 15/5062 20130101; G03G
2215/00561 20130101; G03G 2215/00586 20130101 |
Class at
Publication: |
399/394 |
International
Class: |
G03G 15/00 20060101
G03G015/00 |
Claims
1. A method providing automatic self-calibration of media
registration for image placement on at least one media sheet using
a built-in duplex media path, said method comprising: providing a
printing system including a registration system including at least
one registration sensor, a duplex media path, a printer controller,
a calibration image and a calibration algorithm; registering at
least one media sheet based on registration system data and
correcting media sheet orientation and placement as needed; placing
the calibration image on said at least one media sheet after
registration; inverting the at least one media sheet in the duplex
media path, and re-feeding said at least one media sheet into the
registration system; and detecting and measuring placement accuracy
of the calibration image on the at least one media sheet using said
registration system, and adjusting one or more system settings as
needed based on the registration measurement data to compensate for
one or more system errors degrading accuracy of image to media
alignment.
2. The method of claim 1 wherein said printer controller adjusts
said one or more system settings as determined by said calibration
algorithm in order to automatically correct said at least one
registration error.
3. The method of claim 1 wherein said at least one media sheet is
fed into a printing mechanism in a print engine such that said at
least one calibration image is applied to said at least one media
sheet.
4. The method of claim 1 wherein said at least one registration
sensor captures image data of said at least one calibration image
of said at least one media sheet.
5. The method of claim 1 wherein said at least one registration
sensor comprises a scan bar and/or single linear array sensor.
6. The method of claim 1 wherein said at least one registration
error comprises a skew error, a process error and a lateral
error.
7. The method of claim 1 wherein said at least one registration
sensor comprises multiple sensors of equivalent or different
types.
8. The method of claim 1 wherein said registration system is
utilized individually for a different size of media or different
type of media or different weight of media.
9. A method for registration self-calibration of an image on at
least one media sheet using a duplex media path built-in to a
printing system, said method comprising: providing a printing
system including a registration system including at least one
registration sensor, a duplex media path, a printer controller, a
stored calibration image and a calibration algorithm; registering
at least one media sheet by adjusting orientation and position of
the at least one media sheet as needed based on registration data
from the registration system; placing at least one calibration
image on the at least one media sheet; inverting said at least one
media sheet within the duplex media path, and feeding the at least
one media sheet back into the registration sensing system;
optionally sensing media edges and re-registering the at least one
media sheet bearing the at least one calibration image in the
registration mechanism; detecting and measuring placement accuracy
of the at least one calibration image on the at least one media
sheet using said registration sensing system, determining if an
image location error exists; and adjusting one or more printer
settings based on calibration algorithm offset values if a
registration error is detected by said registration system.
10. The method of claim 9 wherein said registration
self-calibration is programmed to occur automatically based on user
selected metrics related to printer operation.
11. The method of claim 9, wherein said at least one registration
sensor captures image location data of said at least one
calibration image of said at least one media sheet during the step
of detecting and measuring placement accuracy of the at least one
calibration image on the at least one media sheet.
12. The method of claim 1 wherein said at least one registration
sensor comprises a scan bar and/or single linear array sensor.
13. A system for registration self-calibration of image placement
on at least one media sheet using a built-in duplex media path,
said method comprising: a registration system including at least
one registration sensor and a calibration algorithm, said
registration system adapted to register at least one media sheet
during a system calibration process and measuring location of image
features of at least one calibration image applied on the at least
one media sheet; a duplex media path adapted to invert the at least
one media sheet within the duplex media path and re-feed the at
least one media sheet into said registration sensing region; and
one or more detectors adapted to measure the accuracy of placement
of the at least one calibration image on the at least one media
sheet using said registration system; wherein said system is
adapted to provide data enabling a registration calibration
algorithm to establish registration correction settings in response
to determining one or more registration errors as detected by said
registration system.
14. The system of claim 13, wherein said registration sensing
system is associated with a printer controller wherein said printer
controller is adapted to adjust settings of said registration
calibration in order to automatically correct said at least one
registration error.
15. The system of claim 13 wherein said at least one media sheet is
fed into a printing mechanism in a print engine such that said at
least one calibration image is applied to multiple media sheet
surfaces so that calibration accuracy may be improved by
averaging.
16. The system of claim 13 wherein said registration
self-calibration is programmed to execute automatically based on
printer operation metrics.
17. The system of claim 13 wherein said at least one registration
sensor comprises a scan bar and/or single linear array sensor.
18. The system of claim 13 wherein said calibration compensates for
at least one registration error comprising a skew error, a process
error and a lateral error.
19. The system of claim 13 wherein said method corrects a variety
of error influences such as sensor mounting errors, drive roller
location errors, roller diameter variations, media path drag
errors, misplaced or skewed print head or image trajectory errors,
imaging drum mounting errors, media size, media type, image color
or image distortion due to imaging process.
20. The system of claim 13 wherein said registration system is
utilized individually for a different size of media or different
type of media or different weight of media.
Description
TECHNICAL FIELD
[0001] Embodiments are generally related to digital printing
systems. Embodiments are more particularly related to an automated
method and system for registration self-calibration of image on
media sheets using an auto duplex media path. Embodiments are
additionally related to registration systems with a calibration
algorithm.
BACKGROUND OF THE INVENTION
[0002] In printing industries, images on media such as paper in
digital printing systems can require adherence to stringent quality
standards. Quality of such images on the media should be maintained
throughout printing, finishing and binding processes. The media
should correctly be positioned before applying the image.
Therefore, many printers contain active registration systems that
correctly position and orient media prior to applying images to it.
The purpose of the active registration systems is to properly
register sheets of paper, transparency, card stock or other media.
For example, a sheet of paper can be registered as a pair of nips
such as wheels or rollers so that the image can be rendered in the
appropriate location on the paper sheets. The terms printer or
printers are intended to encompass all forms of imaging devices
such as multi-function printers, FAX machines, copiers and the
like. Media will often be referred to as paper for convenience, but
it is to be understood that other media types are encompassed by
the term paper in context with the present invention.
[0003] In a media registration system, multiple sensors can be
utilized to detect the position and/or orientation of media
relative to a process direction. The process direction can denote a
main direction in which the media progresses. The speed or velocity
of the nips can be represented as functions of time and controlled
in a media registration process. An algorithm is necessary for
controlling the speed or velocity of the nips in order to properly
register the image on the paper sheet. Additionally, computational
hardware can also be required to correct the media registration
errors due to deviation of the paper sheet from an ideal nominal
process velocity when it is moving along a path in the process
direction.
[0004] An active registration system can also correct the media
presentation to the imaging device along three different degrees of
freedom such as process, lateral and skew. In process, the position
of the media should be arranged along the direction in which the
media normally travels in the media path. In lateral, the position
of the media is orthogonal to the direction in which the media
travels. Finally, in skew, the angular rotation of the media is
relative to its nominal orientation. A competent media registration
system can measure the incoming registration error when the sheet
approaches the registration system in order to execute a proper
profile to correct the error along three degrees of freedom. Two
laterally separated point sensors may be utilized to detect the
lead edge of the sheet when it moves underneath the sensors, which
detect the process position and the skew of the sheet. A separate
linear array sensor may be used to detect the lateral position of
the sheet. Conversely, a printer may utilize a single linear array
sensor in order to detect incoming process, lateral, and skew
errors, which avoids the need of additional sensors and may require
more elaborate operational algorithms.
[0005] In addition, calibration of the active registration systems
is also required in order to correctly place the image on the media
because of variations in manufacturing in both the media handling
system and imaging system. Traditionally, the calibration can be
achieved by manually scanning printed images on a flat bed scanner,
which can be integrated or independent of the printer. Such a
manual method needs a human operator to manually move the
calibration image sheets from the output to the scanner.
Additionally, calibration values may need to be inputted into user
interface (UI) of the printer. The calibration can also be achieved
by adding a sensing system in the media path after applying the
image in order to evaluate and correct the image on media
calibration values. The above-mentioned methods can add user
complexity or production cost to a printer due to the necessity of
scanner interaction or the additional sensors.
[0006] A need, therefore, exists for an automated method and system
for self-calibration of image on media sheets using normally
included printer elements and media path functionality, such as a
media duplex function and an active media orientation and position
registration mechanism, which can execute a calibration process
without intervention from an operator or adding additional sensors.
Such improved methods and systems are described in greater detail
herein.
BRIEF SUMMARY
[0007] The following summary is provided to facilitate an
understanding of some of the innovative features unique to the
embodiments disclosed and is not intended to be a full description.
A full appreciation of the various aspects of the embodiments can
be gained by taking the entire specification, claims, drawings, and
abstract as a whole.
[0008] It is, therefore, one aspect of the present invention to
provide for an automated method and system for registration
self-calibration of image on media sheets using an auto duplex
media path.
[0009] It is another aspect of the present invention to provide a
self calibration algorithm using data from the registration system
based on the relationship of a calibration image and media edges to
provide offset correction values to achieve improved image to media
placement registration.
[0010] The aforementioned aspects and other objectives and
advantages can now be achieved as described herein. An automated
method and system for registration self-calibration of image on
media sheets using a built-in duplex media path is provided. Media
misregistration is first determined by detection of a media sheet
during initial sheet registration by the systems registration
system. If misregistration is detected, the sheet is positioned by
the registration mechanism. Once sheet registration is achieved, a
calibration image can be placed on the sheet. The sheet can then be
inverted in the duplex media path and re-fed into the registration
sensing region of the media path where the accuracy of the
calibration image placement on the registered sheet is assessed so
a registration calibration value can be determined using a
calibration algorithm. The registration calibration value is stored
in a printer controller to be applied to media registration in
subsequent print jobs.
[0011] Media sheets can be made available in a media tray in an
ordered manner. For example, a paper sheet can be fed into a print
engine for imaging after determining sheet alignment with a
registration system and then correcting orientation and placement
with a registration mechanism. The registration system can include
a single linear array sensor, which captures image and edge data
from the paper sheet after printing the calibration image on the
paper sheet. Nominally registered media may not enable ideal
placement of the image on the media relative to media edges due to
numerous system, media and image errors or offsets.
[0012] The registration system determines media orientation and
media path position based on sensors that detect the media so the
paper path transport and guide elements can be utilized to
influence media trajectory, positioning and phasing for proper
registration of the media before application of the image. The term
registration system encompasses sensors and the whole media sensing
system as well as transport elements and/or guides that can be
controlled to influence media position and/or orientation. A
calibration value can be used to adjust the data available from the
registration system to correct for system errors or offsets,
thereby improving media registration to image placement accuracy.
The system can utilize the registration system and the duplex media
path in order to automatically self-calibrate registration for
image placement on the media sheets without intervention from the
operator or adding additional sensors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying figures, in which like reference numerals
refer to identical or functionally-similar elements throughout the
separate views and which are incorporated in and form a part of the
specification, further illustrate the embodiments and, together
with the detailed description, serve to explain the embodiments
disclosed herein.
[0014] FIG. 1, labeled as "Prior Art", illustrates a block diagram
of components for a standard registration system typical of many
printing devices;
[0015] FIG. 2 illustrates a schematic block diagram of processes
for a registration system in accordance with features of the
preferred embodiment;
[0016] FIG. 3 illustrates a flowchart of an automated method for
self-calibration of image on the media sheets using the active
registration system and the built-in auto duplex media path, which
can be implemented in accordance with an alternative
embodiment;
[0017] FIG. 4 illustrates a schematic representation of an example
of a calibration image on the paper sheet, which can be implemented
in accordance with a preferred embodiment; and
[0018] FIG. 5 illustrates a schematic view of a flow diagram of an
example printing system with the active registration system and the
built-in auto duplex media path, which can be implemented in
accordance with a preferred embodiment.
DETAILED DESCRIPTION
[0019] The particular values and configurations discussed in these
non-limiting examples can be varied and are cited merely to
illustrate at least one embodiment and are not intended to limit
the scope thereof.
[0020] The present invention mainly focuses on input/output
devices, such as a printing device like a printer, multi-function
printing product or other imaging device, which may include a
data-processing apparatus or capability, as desired. A standard
registration system 100 typical of most printing devices is
illustrated in FIG. 1, labeled "prior art." A standard registration
system can include a media delivery system module 110 having an
input media path 101 associated with it, a registration system
module 130, an image transfer module 120 coupled to an output media
path 102 and a duplex media path 103 providing a route through an
auto duplex system module 140 to the registration system module
130.
[0021] One or more application programs, such as image calibration
application software, can be preprogrammed in the printer or
subsequently "loaded" (i.e., transferred from storage into system
memory) for execution of automatic self-calibration of the
calibration image 400 location on a paper sheet 430, as shown in
FIG. 4, by a data-processing apparatus. Image elements 420 included
in a calibration image 400 may be different than shown in the
example.
[0022] An interface, which is preferably a graphical user interface
(GUI), may be used to control, initiate or program frequency,
timing or other aspects of registration calibrations and/or display
results. In an embodiment, an operating system with user interface
can be implemented as a "Windows" like system or a menu selection
interface, as examples. Calibration image calculations provided via
a software program can include determining registration correction
values based on image placement assessment and may additionally
include operation instructions, such as specific media path
cycling, position correction and image creation. Image alignment or
placement is based on the image location on the media as directly
printed or via the transfer surface of an offset print method such
as an imaging drum. In direct or offset printing, placement of the
image is a function of the relationship of independent media and
image positioning.
[0023] Media is generally intended to pass through a printer along
a fixed path and would travel in exactly this path absent
imperfections, such as media size, system errors and part and
assembly variations. The image is likewise generally laid down in a
fixed region which would position the final image on the media as
intended by the application with an idealized media interface. In
more sophisticated printers, media positioning through the media
feed path is adjustable or correctable so that a more idealized
position and orientation may be attained prior to application of
the image. In some cases it may be possible for image lay down over
a normally fixed region to be adjusted or modified to accommodate
media and system errors or offsets. The following descriptions
pertain to either or a combination of media and image position
adjustments to achieve improved image placement due to system and
process imperfections that degrade desired image to media
alignment.
[0024] Registration, as related to concepts of the present
invention, refers to assessing the position and orientation of the
media along the transport path against the ideal location that
would allow nominal alignment or placement of the image on the
media, data associated with that measurement and the position and
orientation adjustment of the media and/or imaging placement
subsequent to registration assessment and prior to receiving the
image. Adjustment means and sensor or edge detection components
that may be employed for this registration are described in
numerous media handling patents and have become sufficiently
commonplace to omit further description here, particularly since
this invention is not dependent upon the specific processes and
sensors or detectors that may be used. Duplexing, or two sided
printing, is now a common feature of many printers. The duplex path
is an alternate routing of the media back into the imaging region
of the printer where media with only a first side image would
otherwise follow an exit path. Since the normal purpose of the
duplex path is to create an image on the second side of the media,
the media is inverted or flipped side to side. Depending on the
product and media path method, the media may go through this path
with the original leading edge at the front or it may become the
trailing edge.
[0025] FIG. 2 illustrates a schematic block diagram of a
registration system 200 in accordance with features of the present
invention. A registration system 200 is typically incorporated into
a region of the media path ahead of or prior to the imaging or
image application region of the printer. The calibration image
and/or calibration algorithm may be downloaded as needed, or more
preferably, be stored in system memory. An input media path can
feed into a measurement system 210. Scan image data can flow from
the measurement system 210 to the calibration process 220, which
determines registration parameters 250 used in the registration
process 230 to control a correction drive mechanism 240.
[0026] During the calibration process, a registration system 200
can register the media sheet 430 before feeding the sheet 430 into
the imaging region of the print engine. A print engine incorporates
a print head 506, as shown in FIG. 5. The print head 506 generates
a calibration image on the drum 508 where it is then transferred
onto the paper sheet 430 passing through the system. Then, the
paper sheet 430 can be routed to the duplex media path 511 where
the image side is inverted before being re-fed into the
registration system 200. The registration system 200 can include a
linear array sensor, which detects the placement of the calibration
image, particularly image location features and edges of the paper
sheet 430, allowing image placement offset assessment and
determination of correction values by means of calibration
algorithm. The calibration algorithm may include software
instructions for executing the self-calibration operation.
[0027] The registration system 200 is adapted to detect whether
registration errors such as skew, lateral and process errors are
present and to what extent, in accordance with the instructions in
the calibration algorithm. The registration system, comprising the
registration measurement system 530 and registration mechanism 504
can calculate registration calibration values for the detected
registration errors or offsets of the image relative to designated
edges of the paper sheet 430. The registration sensing system 530
and the print engine can be electrically connected by a printer
controller, which controls various printing functions provided by
the printing device 100. The printer controller can make
adjustments to the registration calibration values in order to
correct the registration errors, such as position and angle offsets
from the ideal, or the image on the paper sheet 430. The
registration measurement system 530 and the duplex media path 511
along with a calibration image provided by a printing head 506 and
the method of the present invention, enable automatic
self-calibration of the registration process without intervention
from the operator or adding additional sensors or detectors.
[0028] FIG. 3 illustrates a flowchart of an automated method 300
for image on media registration self-calibration using a duplex
media path. The automatic registration and calibration process
begins within a printing system at the point shown in Block 310.
The media enters the paper path region where orientation and
position registration is assessed, as shown in Block 320. If
misregistration is detected, as shown in decision block 330, the
sheets orientation and position is adjusted, as illustrated at
block 340. As previously referenced, the methods employed to adjust
the position and orientation of the media sheet have become
somewhat commonplace and are not described herein. In offset
printing, the media sheet is fed into the nip of a drum and
pressure or fusing roller where the image created on the drum by
the print head is transferred to the media sheet. The calibration
image referred to in block 350 is created on the media by this
method. The next step, block 360, in the automatic registration
calibration process is to reroute and invert the media sheet
through the duplex media path. As the media progresses through the
duplex path, it may again be registered (optional) but this time
the original or first pass registration, based on media edges, is
compared against the calibration image 106 to determine offsets
from nominal or the ideal, as indicated in block 370. Applying a
calibration image to the second media side during this process is
not required. As shown in block 380, image offsets from the ideal
are determined and used to establish calibration values for the
registration process. When the registration calibration values are
first established or are different from previous values, they are
updated in the control system and retained for future use. The
basic process is then completed as shown in Block 390. It should be
noted that repeating the calibration image and registration
assessment process may increase nominal accuracy, obtainable, as
example by averaging, which may include various weighting
considerations such as quantity, media type, duty cycle, previous
calibration values and the like. Repetition may include applying a
calibration image 106 to the second side of the image in the duplex
process and may also include multiple media sheets, each with at
least a single side calibration image. Different images may be used
for each side or sheet.
[0029] It can be appreciated that the foregoing method 300 of the
invention can achieve automatic self-calibration using the
registration system and the duplex media path without user
measurement input, transferring the sheets to a scanning device or
adding cost and complexity to the printing device.
[0030] It should be appreciated from the foregoing teaching that
the calibration method 300 can correct the image on media
registration error from a variety of sources and offsets or errors
such as sensor mounting errors, drive roller location errors,
roller diameter variations, differences in specific rollers that
influence a media size or range of sizes, media path drag friction
or drag, or other elements affecting accuracy of the registration
system 200. It can also now be appreciated that the calibration
method 300 can also compensate for other registration error
influences and component and assembly tolerances, including those
associated with the imaging process, image content, such as color,
and media size, such as length, width and thickness or media type
having various characteristics, such as material composition,
stiffness, texture or weight. Media size variation encompasses the
different media path rollers used for each given size since that
roller combination may be more significant to registration than the
media width. System errors, component location variations and other
errors or offsets, such as those mentioned, contribute to an
overall result that influences image location relative to media
edges. When the sensed image position is assessed against the
sensed media edges, all offset or location errors seen by the same
sensing device are encompassed in calculating the required
registration correction. The terms offset and errors in context
with registration and registration calibration are to be considered
synonymous. The correction therefore applies to all these factors
as they influence the position of the media in the sensed region.
Example: an expected side image edge to media edge relationship, 20
mm as example, may be measured as an actual distance of 19 mm with
a normally registered media sheet due to system errors/offsets. If
this is the result of the registration assessment process, the
automatic calibration can account for this offset by readjusting
the nominal media registered target position by that 1 mm distance,
thereby achieving the desired 20 mm intent in this example. Some
printers in the past have generated some type of calibration image
that had to be manually measured or run through a scanner to
accomplish a calibration correction; this method accomplishes that
correction automatically and quickly.
[0031] Furthermore, such calibration method 300 can be run at any
time without user interaction, since the calibration process can
complete automatically. This can be done periodically based on some
programmed metric, every "n" number of images or weekly or monthly,
or at the beginning of batch jobs, as an example. It may also be
performed at a specific time for a specific purpose as desired. For
instance, an untrained user of the printer 100 can request an image
on media calibration from the printer user interface (not shown)
using the calibration method 300. The calibration process 300 may
utilize more than one sheet in order to arrive at a more accurate
correction and may also be done uniquely or individually for
different sizes of media or different types of media or different
weights of media. For example, a wide format printer may use a
different calibration value for A3 size media than what is used for
A4 size media. Media transport roller spacing may be one critical
factor in establishing registration and registration calibration as
media of some size variations may be influenced by common sets of
rollers where other media sizes are influenced by subsets of those
rollers or by additional rollers.
[0032] FIG. 5 illustrates a schematic representation for processing
a calibration image on the paper sheet 430, which can be
implemented in accordance with a preferred embodiment. As explained
above, the paper sheet 430 includes a lateral edge 402, a first
side lead edge 404, a second side lead edge 406, an inked lateral
edge 414 and an inked lead edge 416. As the paper sheet 430 feeds
from a media tray 501 through a media path 502 into the
registration system 530, the edges are detected as normal to
measure and correct the incoming position and orientation error.
Thereafter, a calibration image is applied on a paper sheet 430
such that a nominal lateral distance 410 is created between the
media lateral edge 402 and the inked lateral edge 414. Similarly, a
nominal process distance 412 can be created between the media lead
edge 404 and the inked lead edge 416. In an example printer, the
built-in duplex media path can invert the media sheet and pass it
again through the registration system 530 and the printing
mechanism 506. When inverted, the image side is on the opposite
side of the sheet 430 from the imaging drum 508, as referenced in
FIG. 5. In an example printer, the duplex media path passes a sheet
430 in the second side transport direction, in which the initial
media lead edge 404 now becomes the trailing edge. A registration
sensor associated with the registration system 530 can detect the
image to non imaged transition region, an edge which is effectively
a definitive location line, as it passes under the sensor, thereby
establishing image location.
[0033] Referring again to FIG. 5, a schematic view of a mechanical
flow diagram for a printing system 500 including the active
registration system 530 and the built-in duplex media path 502 of
the present invention is illustrated, which can be implemented in
accordance with a preferred embodiment. Initially, the paper sheet
feeder associated with a media tray feeds the sheet into the media
path 502 from the media tray 501 into the incoming registration
measurement system 530 via the media path 502. The registration
measurement system 530 measures the incoming registration errors
and makes orientation and position adjustments with the
registration mechanism 504. Registration may be accomplished in
full or in part with components considered part of the media motion
path, but for simplicity any such capability will be described as a
registration mechanism 504. The sheet is then fed into the printing
mechanism 506, where a calibration image is applied to the sheet
430. Then, the sheet 430 travels through the duplex media path 511
and re-enters the registration measurement system 530. During this
pass through, both the sheet 430 edges and the reference edges of
the calibration image are measured by the registration measurement
system 530. Offsets from the intended distance between the
reference edges of the calibration image and the sheet edges are
then determined and by applying the calibration algorithm, become
the registration correction calibration values.
[0034] Calibration values correct for offsets from the intended
image to media position relationship that would otherwise occur
when nominally registered. To briefly recap the previously
described "process", "lateral" and "skew" registrations and in
context with the calibration objective, position of the image on
media in the process direction is its distance from an edge in that
axis of travel, most generally, the top edge based on the image
viewing orientation with measurement determination taken at a point
somewhat near one of the side edges, the left side as example. The
calibration for this value is an amount of offset correction that
would be applied to the nominal registration position of the media
prior to imaging to achieve the intended image to media alignment,
which as referenced, is a distance from a point along the top edge.
The lateral calibration is likewise a distance correction for the
spacing of the image relative to one image side and may be
applicable at one location, 25 mm from a leading edge and along the
left side or typical controlling margin, as example. The skew
calibration is similar to the process offset correction except that
it generally applies, in an example case, at the top edge at the
process measurement point and second point nearer the opposite side
of the media from the process measurement location. If the two
measurements from the top edge are different, that sheet edge is
skewed or angled relative to the feed trajectory. Skew calibration
can provide a compensation for the angular error attained in
nominal media positioning during registration prior to applying the
calibration value. In alternatives, a side edge or regions along a
combination of side and end edges may be used in determining skew.
This may be advantageous for various sizes of media to obtain an
improved aspect ratio.
[0035] In the printer example, the duplex media path 511 not only
inverts or flips the sheet 430 over, but reverses it end for end,
the first side lead edge 404 of the sheet 430 becomes the trailing
edge rather than leading edge. The second side lead edge 406 of the
sheet 430 enters the registration measurement system 530 first, but
it is the original lead edge, now trailing, that is preferably used
for distance measurement relative to the reference edges of the
calibration image. Nominal calibration image orientation and
placement on the sheet can be easily configured for optimization of
the calibration process with an alternative duplex system where the
same edge leads in the first and duplex pass.
[0036] A linear array registration sensor is described in the
present example. This sensor array can span all or portions of the
applicable width of the media and image and therefore is used to
detect process and lateral edges of the media and image target
regions. As the calibration image progresses through the
registration measurement process, the inked lateral edge 414 passes
underneath the registration sensor associated with registration
system 530. The sensor can detect the position of the transition
from light (i.e. white or light paper) and dark (i.e. black, dark
or sufficiently contrasting colored ink), the accuracy of which may
be improved by incorporating a "black" level reference image region
408 in the calibration image. The lateral position of the inked
lateral edge 414 is recorded as the lateral edge of the media, this
data to be used in subsequent calculations for calibration.
Similarly, the inked lead edge 416 passes underneath the
registration sensor when the sheet 430 continues farther through
the registration mechanism 504.
[0037] As the calibration image passes under the sensor, the sensor
can detect the process position of the transition from light to
dark at two or more locations across the inked lead edge 416, the
accuracy of which may be improved based on the black level
reference. The transitions are utilized to calculate the skew and
process position of the inked lead edge 416. The skew and process
positions of the inked lead edge 416 are recorded along with
corresponding edges of the media for subsequent calibration
calculations. Alternate sensor types and configurations are
compatible with the present registration and calibration process.
As example, two simple sensors capable of detecting media edge and
light-dark image transitions can be employed for process and skew
measurement and registration as both are accomplished by passing
the media across a stationary sensor. Such a sensor can also be
used for lateral measurements when mounted to a translation device.
Other stationary sensors can be used for the lateral measurement,
such as a smaller linear array. In another alternative sensor
example, process, lateral and skew measurements may be made with
one or more cameras using known optical pattern recognition
methods.
[0038] Finally, the sheet 430 continues through the printer out
through a media exit path 510. Calibration values, which are the
image registration offsets from nominal, can be calculated using
data from the calibration image and media registration system
measurements with equations (1), (2) and (3).
Skew Error=(first side lead edge skew)-(inked lead edge skew)
(1)
Process Error=(first side media lead edge process position)-(inked
lead edge process position)-(nominal process distance) (2)
Lateral Error=(media lateral edge lateral position)-(inked lateral
edge lateral position)-(nominal lateral distance) (3)
[0039] There are numerous variations to the calibration process. As
example, printing system 500 can apply a different calibration
image 400 to the second side 406 of the sheet 430. Then, the
different calibration image 400 pattern or image elements 420 can
be sensed when the sheet 430 passes through the registration system
530. Therefore, the registration system 530 can achieve two sets of
error measurements for one sheet 430. In this variation, the second
measurement could be compared with the first to establish a
measurement weighting from two different images rather than simply
averaging data from two similar measurements. Another variation
would be to modify the calibration image lay down position for a
second imaging pass based on the calibration error or offset
detected with a first pass so that the image was placed ideally
relative to registered media edges. That calibration image could
then be assessed after a second pass for correct media edge
relationship, with the calibration value further adjusted as
needed. In yet another variation, the calibration image may have
multiple edge transitions that factor into the calculation. Another
variation is to use the leading media edge as the position
reference during the first measurement system pass and the opposite
end edge for the second measurement pass by determining media
length during the first pass. This can be done by assessing travel
distance between the leading and trailing edges.
[0040] It will be appreciated that numerous additional variations
of the above-disclosed elements and methods and other features and
functions, or alternatives thereof, may be desirably employed or
combined into many other different systems or applications. Also
that various presently unforeseen or unanticipated alternatives,
modifications, variations or improvements therein may be
subsequently made by those skilled in the art which are also
intended to be encompassed by the following claims.
* * * * *